If you get the switch panel from another jeep that includes the switch for the factory fog lights, it will connect to the harness that you found with the light harness.
I did this on my 90 jeep. I looked in the engine bay to see what this switch might control. I noticed where the harness for the headlights, turn signal lights etc plugs into the main harness on the drivers side of the engine bay. (It may be covered by your airbox if you still have one) The main harness part had an extra wire coming to it, but the harness that went to the externel lights did not continue this wire. It was the only extra one, and after a bit of testing with a multimeter, it was abvious that the switch that controls factory fog lamps gave +12v to this line. I believe the wire was green, but i can double check if you want me too.
So what i did is i just straight wired in fog lamps to this wire and it worked great. Looking back however, (i should have thought about it but i was being stupid) i needed to put in a relay (im sure a standard 40 amp relay will do depending on what you want to install). After running it this way for some time (maybe 6 months or so) i started to have problems with my headlights. Turns out that my dimmer switch (the one that you use to turn the headlights on (there are too you know)) was overheating. It got so hot that it melted the wiring harness to it.
I would definetely recommend putting a relay in (and of course a fuse from your battery to this relay), but other then that it should be ready to rock and roll.
Feel free to ask any questions you may have... i hope this helps!